Method of making thermocouples



Jam 5, 1954 D. H. MacDoNALD METHOD OF' MAKING THERMOCOUPLES 2Sheets-Sheet l Filed June 4, 1951 Jan. 5, 1954 D MaoDONALD 2,665,322

METHOD OF MAKING THERMOCOUPLES Filed June 4, 1951 2 Sheets-Sheet 2Patented Jan. 5, 1954 STATE essere Dennison H. MacDonald, East Haven,Conn., assignor to Revere Corporation of America, Wallingford, Conn.,

a corporation of Connecticut Application .lune 4, 1951, Serial N o.229,704

(Cl. 13G- 4) 7 Claims.

to a method of making This invention relates thermocouples.

It is a broad object of the present invention to provide method ofmaking a thermocouple which is easier to manufacture and costs less, yetis more reliable in operation and less impaired by even rough usage overa longer period, than previous thermocouples.

It is anothel` object of the present invention to provide method ofmaking a thermocouple of which the insulated electro-conductive strandsof dissimilar compositions are connected with each other by solidifiedelectro-conductive metal which joins and is fused to insulation-baredlengths of the strands, thereby to obtain a simple and strong connectionbetween these strands which will safely withstand for an indefinite timethe usual and even exceptional stresses to which the thermocouple may besubjected in its use.

A further object of the present invention is the provision method ofmaking a thermocouple of this type of which Vthe various connectionsbetween the strands are in the form of inexpensive and easily appliedsolder joints.

Another object of the present invention is to provide method of making athermocouple of this type of which the electro-conductive strands havecoatings of nylon which in the immediate vicinity of the connectionsbetween the strands of dissimilar compositions are fused together by theheat accompanying the application of the strand-connecting solidifiedmetal, so that these fused-together nylon coatings reenforce theconnections between the strands of dissimilar compositions.

It is a further object of the present invention to provide athermocouple of this type of which all the strands are twisted-togetherinto a rope and adjacent lengths of the strands of dissimilarcompositions at spaced intervals longitudinally of the rope areindependently intertwisted prior to their connections intermediate therespective intertwisted strand lengths, so that the latter will, byvirtue of their intertwist, further reenforce the connections betweenthe strands, and will furthermore be held against untwisting by theseconnections.

It is another important object of the present Vinvention to devise amethod of making thermocouples of this type eiiiciently and at very lowcost, not only by the easy and quick connection of adjacent lengths ofthe conductive strands of the thermocouples with solder, but also byeliminating the heretofore imperative and tedious task of baring thesestrand lengths preceding their connection and instead removing theinsulation therefrom solely by the effect of the heat required by and inthe course of the application of the solder thereto.

Other objects and advantages will appear to those skilled in the artfrom the following, considered in conjunction with the accompanyingdrawings.

in the accompanying drawings, in which ce1'- tain modes of carrying outthe present invention are shown for illustrative purposes:

Fig. l is an elevational View, broken away in part, of a thermocouplemade by a method embodying the present invention;

Figs. 2 and 3 are enlarged cross-sections through the thermocouple takenon the lines 2 2 and 3 3, respectively, of Fig. 1;

Fig. 4 shows an intermediate length of the partly-nished thermocoupleunwound for the connection of certain electro-conductive strandsthereof;

Figs. 5 and 6 show progressive steps in making a connection betweencertain electro-conductive strands of the partly-finished thermocouple;

Fig. 7 shows an intermediate length of a partlyfinished thermocoupleembodying the present invention in a modified manner;

Fig. 8 shows the partly-linished modied thermooouple of Fig. 7 in anadvanced stage of its manufacture; and

Fig. 9 is an enlarged section taken on the line 9-9 of Fig. 8.

Referring to the drawings, and more particularly to Figs. 1 to 3thereof, the reference numeral it designates a thermocouple which is inthe form of a composite rope and comprises, in the present instance,seven thermocouple strands which are spirally twisted together. One ofthe strands, designated by the reference character Ii, is in the form ofan electro-conductive wire of a composition which differs from that ofany of the remaining electro-conductive wire strands designated by thereference characters I2. The wire strands I2 may all be of the samecomposition.

Each of the wire strands Il and I2 is provided with an insulatingcoating i3 which serves to insulate each conductive wire strand from theothers, and the gathered and spirally-twisted strands il and I2 arefurther provided with an external insulating coating M which serves asadded insulation to shield the strands li and l2 externally.

As above mentioned, the wire strand ll is of a composition which differsfrom that of the aceaeae ther Wire strands I2 to thus provide, inaccordnce with well-understood thermocouple priniples, anelectro-potential therebetween which aries with circumambienttemperatures. By lay of example, the wire strand il may be an ,lloy ofapproximately 40% nickel and 60% copler, while the other wire strandsmay be formed f straight copper. Of course, many otherslectro-eonductive materials may be used for the vire strands II and I2Without affecting the ,cope of the present invention. y

The coatings I3 on the individual wire strands I and I2 may be formed ofany suitable insu- .ating material which preferably has a melting pointin the neighborhood of that lof solder to Je used for the connection ofthe wire strands as hereinafter described. In the presentA instance,nylon is preferred for the coatingshIS, dwing to its resistance torelatively high temperatures and other desirable characteristics.Preferably, also the coatings I3 of the respective wire strands aregiven different colors so as to be readily identiiied anywhere in thethermocouple. The 'aforementioned external protective coating I4 of thethermocouple is also preferably formed of nylon since the latter has thedesirable characteristics of combining flexibility,moisture-impermeability and abrasion resistance.

vPursuant tothe objects of the present invention, the insulation-coatedwire strands II and I2 are, in the preferred manufacture of thethermocouple I0, first gathered and spirally twisted together so as toforma rope I6 of substantial length. In order to obtain theelectro-potential between the wire strand II and the respective wirestrands I2 at different points longitudinally of the rope It, the strandII is electro-conductively connected with the strands I2, respectively,at longitudinally spaced intermediate points of said rope I6. Sincethese connections may be identical in every respect, the formation ofone of these connections, namely the connection I3 between the strandsII and I2', will be sufficient for an understanding of all connections.Thus, lassuming that the connection I8 between the strands I I and I2 isto be made at a point intermediate the ends of the rope I6, the latteris unwound over a length extending to both sides of the point mentionedand the unwound portions of the strands Ii and I2 are spread apart asshown in Fig. 4. Thereupon, the strands I I and I2 to-be-connected areseparated from the remaining strands I2 and bent into fclose proximityto each other. Next, heat is lapplied to a length of theclosely-adjacent strands I I and I2 in order to remove, by melting, thecoatings I3 thereon. Since the coatings I3 are in this instance formedof nylon which meltsI at a temperature required for ordinary solderingpurposes, there may be held against the closely adjacent lengths of thestrands II and I2', for the removal of the coatings I3l thereon, asolder iron 2Q (Fig. 5) which is heated to a temperature requisite formelting and flowing solder. On the application of heat, in the presentinstance the hot solder iron 2D as explained, the nylon-coatings .I3will quickly melt and run offl theclosely proximate lengths of thestrands II and I2', leaving these strand lengths bare (Fig. 6) for theimmediate reception of solder from a solder wire or rod 2I which is heldagainst the iron 20, the melting solder being applied and spread by theiron over the bare strand lengths (Fig. 4). The nylon-coatings I3 meltand ow off so rapidly that the solder iron need be applied only voncestrands II and 4 to the lengths of the strands II and I2 to be connectedboth for melting away the `coatings I3 and immediately thereafterapplying the solder thereto. The solder thus applied forms between thestrands II and I2' a permanent electro-conductive connection which willsafely withstand for an indefinite time the usual and even exceptionalstresses to which the thermocouple may be subjected in its use. Theconnection I8 is also complete in that the connected lengths of thestrands II and I2 are embedded or substantially embedded in the solderapplied thereto. Moreoventhe solder connection I8 is continuous with theinterrupted coatings I3 on the I2', wherefore no portions of the latteryare left bare. By reason of the heat accompanying the application ofsolder for forming the connection I8 between the strands I I and I2 asexplained, substantial lengths of the nylon-coatings on these strandswhich immediately flank the connection I8 become fused together asindicated at 22 in Fig. 4, thereby consider# ably reenforcing theconnection I8 against rupture or breakage.

vAfter solidification of the applied solder, which takes place shortlyVafter its application, the rope I6 may conveniently vbe stretched so asto contract the spread intermediate, portions of the strands IIA and I2into'V the bodyof the rope, whereupon the contracted strand portions maybe twisted so as to conform to the general twist of the strands in thethermocouple.

The electro-conductive connections between the strand H and thelrespective other strands I2 may be made in exactly the samefashion' asdescribed above in connection with the connection I8 between the strandsII and I2'. After all connections between the strands II and `I2 larethus made, the external coating I4 maybe applied to the rope I6. Thismay convenientlybe accomplished by extruding nylon on the rope I6 as thelatter passes through an extrusion die.

It follows from the preceding that the manu? facture of the instanttherrnocouple is extremely simplel and inexpensive and requires little,if any,

special skill on the part of the manufacturing personnel. Thus, theremoval of the insulation from the therrnocouple strands by the heatrequired for making the Various solder connections between themeliminates the heretofore imperative tedious and time-consuming task ofstripping insulation from these strands prior to their connection.Moreover, the instant thermocouple is, by virtue of the permanentVsolder conL nections between the various strands thereof, and the fusednylon-coatings on the .latterl in the immediate vicinity lof theirsolder connections, valso more reliable in operation and less impairedby even rough usage over a long period of time, than previousthermocouples.

l Reference is now had to Fig. '7 in which the lengths of the strands IIand I2' are, after their separation from'the adjacent lengths of theremaining strands I2,twisted together in dependently of the. latter asya modified step in the manufacture of the thermocouple. .Thereupon,heat is applied to anintermediate portion of the intertwisted strandlengths II and I2," to remove the nylon-coatings on said intermediateportion and apply solder thereto to form the connection I8 (Figs. 8 vand9) in the same or similar manner explained` hereinbefore. Thenylon-coatings on the strands I'I and I2' will, under the heat appliedfor forming the solder connection I8, become fused together for 'somedistance on opposite sides of the connection I8', as is indicated at 22'in Fig. 8. The instant modified thermocouple may then be finished thesame as the previously described thermocouple, and the connections IS inthe instant modified thermocouple are even further reenforced againstrupture and breakage by the described intertwist of the strand lengthsin which the connections IS' are provided.

The invention may be carried out in other specic ways than those hereinset forth without departing from the spirit and essentialcharacteristics of the invention, and the present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

I claim:

1. The method of connecting in a thermocouple separateelectro-conductive strands each being coated with insulation having amelting point near that of solder, comprising the steps of bringingintermediate lengths of said strands, respectively, into close proximityto each other; applying heat to the closely proximate strand lengthspreliminary to joining them with solder, thereby melting away theinsulation on said intermediate strand lengths; and applying moltensolder to said closely proximate strand lengths while the latter arestill hot, so that the applied solder and melted insulation, whensolidied, will join said proximate strand lengths permanently.

2. The method of connecting in a thermocouple separateelectro-conductive strands each being -coated with insulation of amelting point near that of solder, comprising the steps of holdingintermediate lengths of said strands, respectively, in close proximityto each other; holding a hot solder iron in heat-exchange relation withsaid closely proximate strand lengths to heat them preliminarily tojoining them with solder, thereby melting off the insulation coating onsaid strand lengths; and applying solder to the hot iron, while thelatter is held in heat-exchange relation with said closely proximatestrand lengths, for deposition of the solder on the latter to form apermanent connection therebetween.

3. The method of connecting in a thermocouple separateelectro-conductive strands each being coated with insulation having amelting point near that of solder, comprising the steps of spirallytwisting together intermediate lengths 0f said strands, applying heat toan intermediate portion oi' said twisted-together strand lengthspreliminary to joining them with solder, thereby melting away theinsulation on said intermediate portion of the twisted-together strandlengths and fusing together the insulation on said twisted-togetherstrand lengths immediate adjacent said intermediate portion thereof; andapplying molten solder to said intermediate portion of thetwisted-together strand lengths while the same is still hot.

4. The method of connecting in a thermocouple two single ones of amultiplicity of electro-conductive strands which are gathered into arope and each of which is coated with insulation of a melting pointlower than that of solder, comprising the steps of laterally drawingadjacent intermediate lengths of said two strands out of the ropeformation of the adjacent lengths of the remaining strands; bringingintermediate portions of said drawn-out strand lengths into closeproximity to each other; applying heat to said closely proximate strandportions preliminary to joining them with solder, thereby melting awaythe insulation on said closely proximate strand portions; applyingmolten solder to said closely proximate strand portions while the latterare still hot for permanent connection of said strand portions; andre-gathering said intermediate lengths of said two strands with theremainder of the rope after substantial solidication of the moltensolder applied.

5. The method of connecting in a thermocouple two single ones of amultiplicity of electroconductive strands which are gathered into a ropeand each of which is coated with insulation of a melting point lowerthan that of solder, comprising the steps of laterally drawing adjacentintermediate lengths of said two strands out of the rope formation ofthe adjacent lengths 0f the remaining strands; spirally twistingtogether said drawn-out strand lengths; applying heat to an intermediateportion of said twistedtogether strand lengths preliminary to applyingsolder to said portion, thereby melting away the insulation on saidintermediate portion of the twisted-together strand lengths; applyingmolten solder to said intermediate portion of the twisted-togetherstrand lengths while said portion is still hot; and 11e-gathering saidtwistedtogether strand lengths with the remainder of the rope aftersubstantial solidication of the molten solder applied.

6. The method of connecting in a thermocouple two single ones of amultiplicity of electro-conductive strands which are gathered into arope and each of which is coated with insulation of a melting pointlower than that of solder, comprising the steps of laterally drawingadjacent intermediate lengths of said two strands out of the ropeformation of the adjacent lengths of the remaining strands; spirallytwisting together said drawn-out strand lengths; holding a hot solderiron against an intermediate portion of said twisted-together strandlengths preliminary to applying solder to said portion, thereby meltingaway the insulation on said intermediate portion of the twisted-togetherstrand lengths; applying solder to the hot iron, while the latter isheld against said intermediate portion of the twisted-together strandlengths, for deposition of the solder on said portion to form apermanent connection between the strand parts thereof; and re-gatheringsaid twisted-together strand lengths with the remainder of the ropeafter substantial solidication of the molten solder applied.

7. The method as set forth in claim 6, in which said hot iron is heldsubstantially continuously against said intermediate portion of thetwistedtogether strand lengths for the removal of the insulation fromand the subsequent application of solder to said portion.

DENNISON H. MACDONALD.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,365,465 Isles Jan. 11, 1921 2,216,835 Hume Oct. 8, 19402,250,156 Ferguson July 22, 1941

